The present invention relates to a seal for a rolling bearing, and specifically, a seal for a rolling bearing to be used as a closed seal for a rolling bearing.
Rolling bearings, especially small-sized ones used in office equipment, etc., are sealed with a seal fit into an annular seal groove made in the fixed outer race in order to prevent a lubricant, such as grease, from leaking outside.
A seal for a rolling bearing is required to be rigid in its core portion so as to maintain its shape and be flexible in at least its outer peripheral portion which is to be fitted. into the seal groove and also to maintain the sealing effect for an extended period of time without creep.
From this viewpoint, a seal comprising a core made of metal and the inner and outer peripheral parts, inclusive of the sealing part, made of rubber is well known in the art (hereinafter referred to as a first conventional technique). According to the first conventional technique, as shown in the flow chart of FIG. 23, a rubber material and prescribed compounding additives are weighed in weighing step 51 and kneaded in kneading step 52, and the compound is calendered in calendering step 53 to prepare an unvulcanized rubber sheet. On the other hand, a metal material is pressed in press working step 54 to prepare a metal core of prescribed shape, which is washed in washing step 55. A prescribed adhesive is applied to the metal core and baked in adhesive application step 56. The unvulcanized rubber sheet from the calendering step 53 and the metal core from the adhesive application step 56 are put in mold and formed into a prescribed shape to obtain a seal.
Seals of this type also include those made of synthetic resins. For example, JP-A-U-5-96549 (the term xe2x80x9cJP-A-Uxe2x80x9d as used herein means an unexamined published Japanese utility model application) discloses a seal for rolling bearings shown in, FIG. 24, in which a central portion 58 on the inner side (the side facing rolling elements) is made of a reinforced resin plate having higher rigidity than a peripheral portion 59 comprising an inner peripheral portion 59a and an outer i peripheral portion 59b, and part of the inner peripheral portion 59a is made thinner so as to have greater flexibility than the outer peripheral portion 59b (hereinafter referred to as a second conventional technique). The seal of the second conventional technique is press-fit into the annular space formed between the outer and inner races by once deflecting the inner peripheral portion 59a outward and then pressing inward.
Another synthetic resin seal is disclosed in JP-A-6-313436 (the term xe2x80x9cJP-Axe2x80x9d as used herein means an unexamined published Japanese patent application), which is made up of peripheral portions 60 and 61 comprising a relatively soft resin and an intermediate resin portion 62 connecting the peripheral portions 60 and 61 and comprising a relatively hard material (hereinafter referred to as a third conventional. technique). The intermediate resin portion 62 made of at synthetic resin provides a rigid annular insert, and the peripheral portions 60 and 61 are made of a mixture comprising an elastomer and the same synthetic resin as used for the annular insert. The peripheral portions 60 and 61 and the annular insert are molded simultaneously.
However, the first conventional technique has poor productivity because of involvement of complicated production steps as explained above.
When the seal of the second conventional technique is press fit into a rolling bearing, the outer peripheral portion 59b is pulled up, which may result in separation between the central portion 58 and the inner and outer peripheral portion 59 if the bonding strength of the joint surface is weak. Since the central portion 58 made of a reinforced resin plate is merely covered with the inner and outer peripheral portion 59, the seal can be deformed in long-term use. If the bonding strength between the central portion 58 and the inner and outer peripheral portion 59 is weak, the former can be separated from the latter due to a difference in coefficient of linear expansion between them. In any case, the sealing performance will be impaired.
According to the third conventional technique, the material of the peripheral portions 60 and 61 is prepared by kneading at least two resins, i.e., an elastomer and the same resin as used for the intermediate resin portion 62 (annular insert). This leads to an increase in material cost. If the ratio of the elastomer in the resin mixture is increased, the peripheral portions 60 and 61 have improved flexibility but have poor adhesion to the intermediate resin portion 62. If, on the other hand, the ratio of the elastomer is decreased, the peripheral portions 60 and 61 are too hard and stiff, thereby resulting in poor sealing performance.
The present invention has been completed in the light of the above-described problems of conventional techniques. Accordingly, an object of the present invention is to provide a seal for rolling bearings which does not undergo separation between the core portion and the peripheral portion thereof or deformation in long-term use and thereby exhibit improved sealing properties for an extended period of time.
The object of the present invention is accomplished by a seal for a rolling bearing comprising a flexible resin portion which comes into contact with at least one of the seal grooves on inner and outer races and a rigid resin portion which is more rigid than the flexible resin portion, wherein the rigid resin portion and the flexible resin portion are fusion bonded together into an integral body.
In the present invention, because a flexible resin portion and a rigid resin portion that can be fusion bonded to each other are used, they are firmly joined together without using an adhesive or a like means.